Heat stress has been a problem for military personnel since armies first operated in hot environments. Greek and Roman soldiers suffered from the heat in addition to the physical burden imposed by the weight of body armor and weapons whenever they fought in the Middle East or Southwest Asia. Today's warrior faces the same problem; a combination of physical workload and lack of cooling diminish the performance of highly trained individuals. For example, during the 1967 war between Israel and Egypt, the Egyptian army sustained over 20,000 heat casualties.
The advent of chemical and biological warfare has created an increased thermal burden by requiring the use of cumbersome or encapsulating garments. Military units and First Responders attempting to conduct missions in such garments, particularly in hot environments, often find their physical endurance greatly diminished and cognitive functions impaired. Available resources are often overtaxed by demands on logistic support for such things as excess potable and cooling water, and the increased numbers of personnel that are needed to accommodate extended rest periods that are required by exhausted personnel.
Similar problems exist in the civilian sector. For example, foundry workers, chemical plant operators, and warehouse workers often find themselves limited in their capacity to perform tasks in hot climates. Mining is notorious for placing sometimes life-threatening thermal burdens on deep shaft miners (e.g., South African gold miners). On the other hand, extremely cold environments produce similar difficulties. Divers, winter sportsmen, and persons living in northern latitudes often encounter cold conditions that may induce hypothermia.
Various approaches have been adopted to reduce heat and cold stress. The simplest approach has typically been to impose well defined work/rest cycles which limit an individual's exposure time and allow for cooling-off (or warming-up) rest periods. This is often successful in minimizing fatigue and illness but severely constrains productivity and may threaten successful task performance if manpower is limited. Passive cooling systems have sometimes been employed to mitigate heat and cold stress. Passive cooling systems, such as water-soaked clothing items or ice vests are a comparatively low cost approach but provided only a limited amount of cooling. Passive heating systems such as extra layers of clothing are also comparatively low cost, but they loose their effectiveness if they become moist with perspiration, and can in fact induce hypothermia if the temperature drops.
There are many further needs for efficiently heating and cooling materials and objects such as electronic components, car seats, plants, and animals that are often inadequately addressed by present techniques. What are needed therefore are improved systems and garments for providing thermal management of persons and objects in very hot and very cold environments.